2011-08-08_GENERAL DOCUMENTS - C1981008

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but results from other regions show improved WUE with this irrigation method. Putnam et al. (2005) showed significant waxer savings from partial season irrigation of alfalfa in the Klamath Basin and Sacramento Valley of California with few long-term impacts on alfalfa stands. However, for arid climates and sandy . soils, summer termination of irrigation can reduce alfalfa stands and biomass yields after irrigation is resumed (Ottman et al., 1996). More information is needed about partial season irriga- tion in the Great Plains and Intermountain West regions. Management Factors Affecting Alfalfa Water -Use Efficiency Variety While it is expected that alfalfa varieties would vary widely in WUE, there is little evidence to support this. A Utah line- source irrigation study evaluated WUE of alfalfa varieties `Ladak', Washoe', and `Mesilla with fall dormancy ratings of three, five, and seven, respectively (Recta and Hanks, 1980). The 2 -yr study found no difference in biomass yield or water use among variet- ies. A line- source irrigation study in Texas (Undersander, 1987) examined WUE of alfalfa varieties `Vangard', `Cody', `Zia', and Dawson', all with varying dormancy characteristics and diverse genetic backgrounds. Results showed no significant differences in WUE among the varieties for any level of irrigation. Hattendorf et al. (1990) conducted a line- source irrigation study in Washington comparingwater use and biomass yield of alfalfa varieties `Vernal', `Vernema, and 'CUP 101' with fall dormancy ratings of two, four, and nine, respectively. No differences in biomass yield or water use were found. A line- source irrigation study conducted in California (Grimes et aL, 1992) evaluated WUE of alfalfa varieties 'CUP 101', ` Moapa 69', and `WL 318' with fall dormancy ratings of 9, 8,and 3, respectively. In the California environment, the semi - dormant `WL 318' had a slightly higher WUE than the other two varieties during the cool spring conditions. During the hot sum- mer conditions, the less dormant CUF 101 and Moapa 69 varieties had higher WUE. However, there was no significant difference among varieties when WUE was evaluated on a total season basis. These studies indicated that alfalfa varieties with varying dormancy traits and genetic backgrounds did not differ greatly in total- season WUE. Varieties with different fall dormancy may not relate to the suitability of the variety under deficit irrigation. Less is known about the potential role of alfalfa variety on partial season irrigation. It has been reported that alfalfa varieties that have cold tolerance and winter hardiness also have drought tolerance because both conditions desiccate plant cells (Jung and Larson, 1972). Drought and cold tolerance may be linked to small cell size. If advantages in WUE during particular periods of the growing season do exist, selecting varieties that possess drought tolerance and are more dormant may be best for stand survival during dry periods in a partial season irrigation system. More studies are needed to evaluate alfalfa varieties under partial season irrigation in different envi- ronments. It is thought that a more fibrous root system may be more efficient in extracting soil water than a dominant tap root system. However, it should be noted that numerically high fall dormancy ratings tend to be correlated with tap - rooted alfalfa varieties and low fall dormancy ratings are correlated with fibrous- rooted alfalfa varieties (Smith, 1993). Table I. Average total season biomass yield, evapotranspi- ration (ET), and water -use efficiency (WUE) from studies of alfalfa under variable irrigation in the Great Plains and Intermountain West of the United States. Author Location Treatment Yield ET WUE Mg ha I cm Mg ha I cm I Daigger et al., NE full irrigation 11.5 151.7 0.08 1970 Bauder et aL, 1978 Retta and Hanks, 1980 ND dryland 5.8 33.9 0.17 deficient 9.7 60.2 0.16 optimum 10.3 64.5 0.16 excessive 10.8 68.6 0.16 average 9.2 56.8 0.16 UT line source 7.2 38.3 0.19 average 8.0 37.6 0.21 9.3 47.7 0.20 10.7 55.4 0.19 11.9 57.4 0.21 12.5 61.6 0.20 9.9 49.6 0.20 Sammis, 1981 NM line source average Carter and MN high Sheaffer, med. high 19831 med. low dryland average Undersander, TX line source 1987$ average Wright, 1988 ID full irrig. Bogler and TX average Matches, 1990 Smeal et al., NM line source 1991 average all full irrigation defict irrigation dryland 6.0 66.7 0.09 8.3 77.6 0.11 0.0 78.5 0.13 1.5 90.9 0.13 2.3 92.5 0.13 3.1 03.8 0.13 4.3 09.4 0.13 5.0 17.5 0.13 7.0 24.5 0.14 9.6 35.2 0.15 22.1 45.7 0.15 13.7 04.0 0.13 7.4 32.6 0.23 7.0 29.9 0.23 5.5 26.4 0.21 2.1 17.9 0.12 5.5 26.7 0.21 13.5 76.2 0.18 22.6 113.0 0.20 16.4 91.7 0.18 17.5 93.6 0.19 14.7 94.2 0.16 na§ na 0.17 3.0 45.8 0.07 6.0 63.1 0.09 8.7 78.5 0.11 12.3 91.3 0.13 15.1 104.9 0.14 14.8 106.7 0.14 12.5 . 93.7 0.13 10.3 83.4 0.12 Overall averages All authors all All authors all All authors all All authors all t Harvests 3 and 4 only reported. 1 Maximum yield and ET only reported. § na, not applicable. Harvest Timing Harvest timing has been found to influence alfalfa WUE. A study conducted in New Mexico from 1981 to 1987 by Smeal et al. (1991) evaluated the WUE response of alfalfa in relation to the accumulation of growing degree -days (G within each 12.8 88 0.16 16.6 91 0.19 11.1 80 0.17 6.0 39 0.14 Agronomy Journal • Volume 103, Issue 1 • 2011 47